Downhole tool

ABSTRACT

A downhole tool comprising: an axial drive unit ( 10 ) having a connection for an electric power cable extending up the borehole, and including an anchoring mechanism ( 12, 16 ) operable in the borehole between a first configuration in which the anchoring mechanism resists rotational and axial movement of the unit, and a second configuration in which the anchoring mechanism is moveable axially in the borehole, an axial drive mechanism that moves the anchoring mechanism axially down the borehole when in the second configuration; a motor ( 28 ) mounted on the drive unit at the downhole end thereof; an hydraulic pump ( 30 ) connected to the motor, the pump providing a source of hydraulic power; and a functional unit connected below the hydraulic pump and powered thereby, operation of the axial drive mechanism acting to move the functional unit axially down the borehole.

The present invention relates to downhole tools, in particular tools that are used in boreholes such as oil, water or gas wells, or the like.

In the construction and treatment of underground boreholes there are a number of basic techniques that are used for the conveyance and operation of tools in the borehole. In drilling, for example, a drill bit is fixed at the lower end of a drill string formed from a series of hollow drill pipes connected end-to-end. By rotating the drill string at the surface, or by using a downhole motor, the bit is caused to rotate and this, together with weight applied to the bit allows drilling to progress. To remove the drilled material and assist in the drilling process a drilling fluid, typically known as “mud”, is pumped down the inside of the drill string to exit at the drill bit and carry drilled material (“cuttings”) back to the surface in the annulus around the outside of the drill string. The drilling fluid also provides support to the borehole and balances the pressure of fluids in the formation due to the hydrostatic pressure created by the column of fluid. In a development of this technique, a motor, typically in the form of a Moyno (positive displacement) device is installed in the drill string just above the bit. The motor is driven by the flow of mud and can be used to rotate the drill bit independently of the rotation of the drill string. This technique, in combination with a bent downhole assembly (“bent sub”) and an orientation sensor allows the direction of drilling to be controlled. For straight drilling, the technique of rotating the drill string is used (“rotary drilling”) together with rotating the drill bit with the motor. To change direction, rotary drilling is stopped, the bent sub is oriented so that the bit face points towards the intended direction by rotating the drill string from the surface and drilling recommenced using the downhole motor to rotate the bit and by applying weight to the bit from the surface through the drill string (“sliding mode drilling”). When the borehole has attained the desired direction, rotary drilling recommences.

Measuring devices can also be provided in the lower part of the drill string (“bottom hole assembly” or “BHA”). These devices, for example measurement while drilling (“MWD”) devices for measurements relating to the drilling processes: weight on bit, ROP, direction and inclination, or logging while drilling (“LWD”) devices for formation-related measurements: resistivity, nuclear measurements, acoustic measurements, can provide data to the surface via memory devices removed when the BHA is withdrawn from the borehole, via an electric cable running inside the drill string, or by mud-pulse telemetry in which pressure pulses created in the drilling mud by means of a siren located in the BHA are detected at the surface.

Any activities that involve the use of a drill string require the presence of a drilling rig at the surface. Also, the time taken to run the string into and pull the string out of the well is relatively long, especially in very deep wells.

Once the borehole has been drilled, measuring devices can be lowered into the borehole on cables that provide electric power and data communication (“wireline”, “electric line”, “slick line”) between the downhole tool and the surface. Such operations do not require the use of a drilling rig and can be conducted relatively quickly. However, to date it has only been possible to conduct drilling operations using a wireline unit on a small scale in view of the difficulty in providing power, torque and weight on bit downhole. Coring is one example of a drilling activity that has been conducted by a wireline system. In coring, a cylindrical drill bit is used to extract a solid core of material from the rock surrounding the borehole which is returned to the surface for analysis. An example of a wireline coring unit is shown in U.S. Pat. No. 4,354,558. Other wireline devices have been proposed for drilling relatively small holes laterally from a main borehole. All of these devices provide only relatively short drain holes and all suffer from the problem of providing torque and weight on bit, especially where it is necessary to drill through metallic casing in the borehole before drilling onto the rock. One approach, as shown in U.S. Pat. No. 6,167,968, involves separating the action of drilling or milling through the casing using a short stiff mill section from the action of drilling into the rock using a flexible drill section. In another technique, the flexible drill shaft is surrounded by a series of discs which provide support and allow pressure to be applied to the drill bit. This is shown in U.S. Pat. No. 6,276,453. Another approach which separates the provision of thrust and torque is shown in U.S. Pat. No. 5,687,806.

EP 1 247 936 describes a wireline tool that can be run inside drill pipe and used to obtain cores by drilling outside the drill string via a side exit mandrel in the bottom hole assembly. In this device, a packer is inflated inside the drillpipe and an electronics an piston sub is positioned above the packer, and a drilling motor and core bit is positioned below the packer. The piston provides weight on the bit by driving through a sliding seal in the packer and torque is provided by diverting mud flow from the inside of the drillstring into the drilling motor below the packer. The drilling mud and cuttings return to the surface via the annulus in the lateral core hole and the annulus in the main hole in the normal manner. The packer in this arrangement serves as a reaction point for the weight on bit and torque applied during the drilling process. It also causes the drilling mud to flow through the motor. However, because it is necessary to provide a sliding seal through the packer, the design is limited in its ability to provide an extended drilling depth. Also, it is essential that there is a supply of drilling mud from the surface and an annulus for the return of the drilling mud and the cuttings.

One particular use of such drilling tools, is that of re-entry drilling in which further drilling operations are conducted in an existing well for the purposes of improving production, remediation, etc. A review of such techniques can be found in Hill D, Nerne E, Ehlig-Economides C, and Mollinedo M “Reentry Drilling Gives New Life to Aging Fields,” Oilfield Review (Autumn 1996) 4-14. One particular tool described is the VIPER Coiled Tubing Drilling System which comprises a drilling head module with connectors for a wireline cable, a logging tool including an number of sensors and associated electronics, an orienting tool including a motor and power electronics, and an drilling unit with a steerable motor. While the system is provided with power and data via a cable, it is also necessary to provide a coiled tubing to push the tool along the well.

It is an object of the present invention to provide a downhole tool that can be run on wireline and which has the ability to provide sufficient weight on bit and torque to achieve effective drilling.

In accordance with the present invention, there is provided a downhole tool comprising: an axial drive unit having a connection for an electric power cable extending up the borehole, and including an anchoring mechanism operable in the borehole between a first configuration in which the anchoring mechanism resists rotational and axial movement of the unit, and a second configuration in which the anchoring mechanism is moveable axially in the borehole, an axial drive mechanism that moves the anchoring mechanism axially down the borehole when in the second configuration; an electric motor mounted on the drive unit at the downhole end thereof; an hydraulic pump connected to the motor, the pump providing a source of hydraulic power; and a functional unit connected below the hydraulic pump and powered thereby, operation of the axial drive mechanism acting to move the functional unit axially down the borehole.

Preferably an orienting unit is positioned below the drive unit that allows axial rotation of at least part of the tool below the drive unit, so allowing any asymmetry in the functional unit to be oriented in a specific direction. A diverting member, such as a kick plate, can be positioned below the functional unit to urge the unit in a predetermined direction on operation of the drive unit to advance the functional unit down the borehole.

The borehole will typically be filed with a fluid and the hydraulic pump can preferably use this as the hydraulic fluid supply which provides the hydraulic power.

The functional unit can have a number of possible functions: drilling, well completion, measurement, stimulation, remediation, etc. and any combination of these functions. Where the functional unit has a drilling function, it preferably comprises a drilling motor that is powered by the hydraulic fluid from the pump. The drilling motor is typically connected to the pump (which is driven by the electric motor) by means of a hollow drill shaft through which the fluid flows and by means of which the drive unit urges the drilling unit forwards. A drill bit can be connected to the drilling motor.

By appropriate use of the kick plate and/or a bent sub in the drilling tool (for example, the bent sub is oriented in a plane substantially perpendicular to that of the kick plate with the bit facing away from the plate), the drill bit can be caused to drill away from the borehole. The extent of drilling away from the borehole is determined by the length of the drill shaft. Preferably, at least one support is provided on the drill shaft to avoid buckling during drilling.

In order to prevent drilled material blocking the well or causing the tool to become stuck, a cuttings catcher can be positioned below the drilling unit and attached to the tool, such that the catcher, typically a bag or storage tube, can be withdrawn from the well with the tool on the wireline cable. Diverters, e.g. rubber cups, can be located above and below the drilling unit to force the cuttings into the catcher. In such a case, it is preferred to provide a circulation tube to allow fluid to circulate back up the borehole one the cuttings have been removed. Alternatively one or more baffles can be provided to direct flow containing cuttings down the borehole below the tool to avoid sticking.

The drilling unit can also include measurement units and, optionally, inflatable packers for providing pressure isolation of parts of the borehole. This latter feature can be useful in making formation pressure measurements using the tool.

An alternative form of functional unit can comprise an completion unit. This will typically comprise a tubular completion member, for example a casing or screen that can be advanced into the borehole, typically with the assistance of a properly positioned kick plate or whipstock, and disconnected so as to remain in place when the tool is withdrawn from the borehole. The completion member can be filled with a completion fluid, for example a cement slurry or gravel pack that is pumped out of the completion member and into the borehole around the completion member by means of the hydraulic pump.

The tool can further comprise a storage unit located in the borehole in which at least one functional unit can be stored when not in use. In such a case, it is preferred that a latching system is provided for disconnecting the functional unit stored in the storage unit from the remainder of the tool.

One further embodiment of the tool comprises an imaging device for locating the portion of the borehole at which the tool is to operate.

The present invention will now be described by way of examples, as shown in the accompanying drawings, in which:

FIG. 1 shows common features of first embodiment of the present invention;

FIG. 2 shows the embodiment of FIG. 1 configured for drilling;

FIGS. 3 a and 3 b shows the embodiment of FIG. 2 in different stage of a drilling operation;

FIG. 4 shows a second embodiment of the invention configured for drilling;

FIG. 5 shows a third embodiment of the invention configured for drilling and measurement;

FIG. 6 shows a fourth embodiment of the invention configured for drilling and pressure measurement;

FIGS. 7 a and 7 b shows a fifth embodiment of the invention configured for completion in different stages of operation and

FIG. 8 shows a sixth embodiment of the invention configured for multiple operations.

Referring now to the drawings, there are shown therein a number of embodiments of the present invention. While these embodiments are all described in the context of an open borehole, it will be appreciated that this can also be a cased borehole, or includes drill string or production tubing. All of these senses are included in the use of the term “borehole”. Also, in the context of a borehole and the arrangement of the tool, the terminology used is “up” for the direction towards the surface, and “down” for the direction away from the surface, even if the borehole in question is not vertical. A first embodiment of the invention is shown in FIG. 1 and comprises a drive unit 10 including a connection for a wireline cable (not shown). The drive unit 10 is essentially a tractor unit such as is described in U.S. Pat. No. 5,954,131. However, in the configuration shown here, it is situated at the top of the tool string and serves to push the tools along the borehole rather than pull them behind it. Futhermore, wiring is provided to allow power and data to be provided below the unit 10.

The drive unit operates by extending locking members 12 positioned at one end of the unit 10 against the walls of the borehole 14. Corresponding locking members 16 are provides at the other end of the drive unit 10, but in this first configuration, these are not locked against the borehole 14. The portion of the drive unit between the locking members 12, 16 comprises and extending and contracting mechanism 18. This mechanism 18 is operated to urge the lower part of the drive unit down the borehole. Once the full extent of the mechanism 18 is reached, the unit is advanced by locking the lower members 16 against the borehole 14, unlocking the upper members 12 from the borehole 14, and contracting the mechanism 18 so as to drag the upper portion of the unit down the well. This cycle can be repeated as often as is required. When it is desired to run the tool into a vertical part of the well, or to withdraw the tool from the well, both sets of members 12, 16 are unlocked and the tool moves down by gravity or is pulled back to the surface by the cable in the usual manner.

Immediately below the drive unit 10 is located an orienting sub 20. This is essentially the same as that used in the VIPER coiled tubing drilling system described above. The orienting sub includes a motor and allows relative axial rotation between parts of the tool above and below the sub.

A control sub 22 is located below the orienting sub 20. The control sub 22 includes a number of functions for control of the tool, including power supply and control, a telemetry system, system control logic and the like.

Below the control sub 22 (or possibly forming part of the control sub 22) is a navigation sub 24. This can include accelerometers, magnetometers, and/or gyros for determining the position and orientation of the tool in the borehole 14. Suitable sensors include the GPIT inclinometer tool of Schlumberger, or the navigation sensors o the VIPER tool described above. The navigation sub can be placed above the orienting sub. In this case, an indexing function is required to register the relative position of the tool parts below the orienting sub relative to the navigation sub.

A pumping unit 26, comprising an electric motor 28 driving a Moyno (positive displacement) pump 30, is located below the navigation sub 24. The sizes and powers of the electric motor 28 and pump 30 are selected according to operational limitations. For example, the power of the motor 28 will be determined by the amount of power available over the wireline cable and the maximum size limitation of the tool string to be able to pass through the borehole, production tubing or the like. The output from the pump 30 will be affected by the power output from the motor 28, the speed of the motor 28, and again, the operational size limitations. The pump has an inlet 32 at its upper end to allow borehole fluid to enter the pump, and an outlet 34 at its lower end from which the fluid is pumped to provide the hydraulic power supply.

The functional unit of the invention is attached at the outlet end 34 of the pump 30. FIGS. 2-7 show a functional unit in the form of a drilling tool. As is shown in FIG. 2, a drill shaft 36 in the form of small diameter drill pipe (e.g. 1.5″) is connected to the output of the pump 30. The length of this shaft will determine the maximum length of any lateral hole drilled-from the main borehole 14. A drilling motor 38 is located at the lower end of the shaft 36. This drilling motor 38 is typically a Moyno device (similar to the pump 30, except that in this configuration, it is driven by the fluid flow entering the motor, arriving from the pump 30 via the drill pipe 36). The drilling motor 38 is typically relatively small (2⅛″ or 2⅜″) and will usually include a bend in the housing as is known in directional drilling practises. It is particularly preferred to use a flex motor with bend housing to build enough angle in a short distance to produce effective lateral holes from the main borehole 14.

A drill bit 40 (e.g. 2.4″) is attached to the drilling motor 38 in the normal manner.

A kick plate 42 is positioned below the drill bit but connected directly to the upper part of the drive unit 10 by means of a support 43. The kick plate 42 comprises a plate or other planar surface that is angled relative to the borehole axis and serves to urge the drill bit against the borehole wall in a specific direction. In operation, the kick plate functions in a similar manner to a whipstock, as will be described below. The support 43 is connected to the drive unit by means of a lockable sliding connection 44. A swivel 46 is provided part way along the support 43 to allow the kick plate 42 to be oriented in the borehole by operation of the orienting sub 20. Functioning of the kick plate 42 is described in more detail below.

In use, the tool is lowered into the well on a wireline cable until the desired depth is reached. At this point the drive unit 10 is locked by operation of the upper locking members 12 and the electrical pumping unit 26 is activated. The fluid (“mud”) from the main well 14 is pumped into the small drill-pipe 36. The mud flows in the drill pipe 36 and reaches the motor 38, which rotates the bit 40.

Before starting drilling, the orienting sub 20 insures that the bend of the drilling motor 38 and the kick-plate 42 are facing towards the proper direction (often called “tool-face”). Axial displacement and weight on bit (“WOB”) are delivered by the drive unit 10.

This combination technique allows the drill-bit 40 to be pushed into the formation and to drill a curved hole thanks to the bent drilling motor 38. The bend angle is chosen so that the lateral borehole 50 turns through 90 degrees over its length (typically around 100 ft) as is shown in FIGS. 3 a and 3 b. Mud circulation in lateral hole 50 is provided by the pumping unit 26 in the main hole 14, via the small drill-string and bit. Cuttings are lifted in the lateral hole 50 and brought into the main hole 14 by the mud and deposited in a cuttings catcher device as described below in relation to FIG. 4.

When the drilling of one lateral hole 50 is completed and if the cutting catcher bag is not full, the wireline electrical drill system can be moved to another depth and another lateral hole can be started.

The kick-plate 42 is a guidance plate disposed at an angle to the axis of the main hole 14. The plate 42 acts as a whipstock to generate side force on the bit 40 and to push the bit into the formation. This kick-plate 42 is typically hung onto the drive unit 10 by a sliding connection 44. The kick-plate 42 can be held at a fixed position in the borehole 14, or at a fixed distance from the static part of the drive unit 10 when starting the kick-off drilling. During the first push displacement of the drive unit 10, after the upper part of the drive unit 10 has been locked in the borehole, the bit 40 is pushed into contact with the kick-plate 42. Once the drill bit 40 has started to penetrate the borehole wall to form the lateral hole 50, the kick-plate 42 may move away from the entry point when the drive unit 10 is repositioned in the borehole 14.

In an alternative, the kick-plate is held by two support tubes parallel to the drill-sting. These tubes slide into the connection 44 on the drive unit 10 and a swivel is used as described above. The connection for the support tubes is attached to the middle or upper section of the drive unit. Sliding movement of the support tube in the connection can be controlled by a lock system in the connection, as follows:

-   -   a) At the beginning of the drilling of a new lateral hole, the         drive unit contracts to bring the upper and lower parts         together, and then locks its upper part in the hole, while         releasing its lower part.     -   b) The locking system for the kick-plate support tubes is         blocked. This fixes the tube with respect to the upper part of         the drive unit     -   c) The drive unit then starts to extend. This pushes the bottom         section (including drill-string) towards the bottom. The bit         hits the kick-plate and a radial displacement is generated,         forcing the bit into the formation.     -   d) When the bit is entered sufficiently into the side formation,         the locking system for support tube can be released. In some         cases, it may be required with some options to keep the         kick-plate at the initial position relative to the borehole         rather than relative to the drive unit during the complete         drilling operation of the lateral hole.

A further embodiment of the invention is shown in FIG. 4 which ensures that well section around the kick plate 42 is hydraulically isolated. This isolation is achieved by two rubber cups 52, 54 (alternatively by two packers) that seal in the borehole 14 above and below the drilling section. This isolation forces the mud flowing out of the lateral hole 50 during drilling to be forced into a cutting catcher bag 56 attached to the lower cup 54. When moving the tool in the wellbore, the rubber cups or the packers are retracted or deflated.

The cuttings catcher 56 comprises a large bag attached at or near the kick-plate 42. This bag collects cuttings brought by the mud out of the lateral hole 50 during drilling. In a preferred arrangement, the bag 56 extends below the kick-plate 42 as is shown in FIG. 4. A filling mechanism allows proper circulation of the cuttings (with mud flow return to ensure proper filling), for example a “bellows” type bag which is attached to the lower cup 54. A circulation tube 58 is attached between the cups 52, 54. The bag 56 is porous so that mud can pass through while cuttings are retained, the mud passing back up the tube 58 and into the borehole 14 near the pump unit 26. Alternative arrangements comprise porous tubes to catch the cuttings in place of the bag, or an arrangement of baffles that direct cuttings down the borehole 14 below the tool if it is not necessary to be able to re-enter the lower part of the borehole.

The drill-pipe 36 between the pump unit 26 and the motor 38 is under compression to transmit axial force from the drive unit 10 onto the drill-bit 40 and ensure Weight-On-Bit (WOB). The diameter of the pipe will typically be small (probably between 1 to 1.75″), and the pipe length can be around 150 ft. Up to 3 tons WOB may be required in some drilling applications. Such an axial load can generate buckling effects in the drill pipe. In large diameter boreholes, large deformations of the drill pipe may occur which can be detrimental to the drill pipe structure and drilling process. To avoid buckling the drill pipe 36 in the large hole section, pipe guides 60 can be installed at various distances along the pipe 36. These guides can comprise cross-shaped members with dimensions similar to the diameter of the main hole. The pipe 36 slides in the guides 60. The guides 60 can be connected to each other by flexible couplings 62 such that the maximum separation is limited. At the upper end, the couplings 62 are connected to the drive unit 10, and at the lower end to the to the kick-plate 42.

WOB is generated by the drive unit 10, which preferably operates at constant force rather than constant speed. It is controlled to reduce WOB quickly when the drilling motor 38 stalls (which can be detected by real-time pump pressure monitoring).

A small logging (measurement) sub 64 can be inserted between the drill-pipe 36 and the motor 38, as is shown in FIG. 5. This sub 64 can have an OD typically around 2 ⅜″ while having a internal bore of approximately 1″ for the internal mud flow. This sub can contain at least the minimum components to support the measurements, and is linked to the control sub 22 below the drive unit 10. Communication can be based on wiring or by wireless telemetry. This control sub 22 controls the measurement sub 64 and transmits data to the surface over the wireline cable

The measurement sub 64 can include the following functions:

-   -   Resistivity measurement. This can be electrode-based         (lateralog), induction coil-based, or toroid antenna-based.         Localized electronics may be provided for measurements while         limiting cross-talk effect.     -   Inclinometer to determine the inclination of the lateral hole.     -   Mini gamma-ray detector.     -   Pore pressure measurement behind the damage zone as is shown in         FIG. 6. An inflatable packer 66 can be provided to isolate the         annulus of the lateral hole 50. A pressure gauge is installed         inside the drill string 36 below the pumping unit 26. During the         measurement, the packer 66 seals the small annulus 50, while the         pump 30 is run in the reversed mode to “empty” the small         wellbore 50 near the bit 40. This allows the measurement of         formation pressure. If the pump 30 used for drilling is not able         to generate a pressure low enough near the bit 40, a piston pump         (not shown)may be used in parallel for large pressure reduction         (a valve is required to isolated the drilling pump).

The integrated logging, drilling methods allows to determine the profile of the logged data versus radial distance from the wellbore. High resolution characterization can be achieved perpendicularly to the main wellbore.

The ability to re-enter in the small lateral hole 50 after withdrawing the tool from the borehole 14 may be important. Since depth and orientation measurements may be insufficient, borehole images may be required (from electrical or ultrasonic imaging tools, such as the FMI, OBMI or UBI tools of Schlumberger). These images allow the operator to visualize the small radial hole (which will appear as a long ellipse in the borehole wall). For this application, the drill system should insure “thoughwiring” so that the imaging tool can be installed below the kick-plate. Logging upwards is initially performed to locate the small hole. When located, the drive unit 10 is used to lower the bit 40 to the proper depth (and at the proper orientation). Improved positioning of the device to re-enter in the lateral and the offset of depth between the imaging system and the device can be measured by the drive unit displacement.

In the embodiment of the invention shown in FIGS. 7 a and 7 b, the drilling configuration of the tool described above is replaced by a completions function. In the case shown, a liner 70, pre-loaded with cement slurry 72 and provided with plugs at the top 74 and bottom 76 is connected at the end of a drill pipe 73 and is run into the hole 14 and advanced into the lateral hole 50 using the drive unit 10 and kick plate 42 in a similar manner to that described above in relation to the drilling function. When the liner 70 is positioned in the lateral hole 50 (FIG. 7 b), the pumping unit 26 is operated to pump the upper plug 74 down inside the liner to force the lower plug 76 out (or to shear a seal at the lower end of the liner) and force the cement slurry into the annulus around the liner 70 in the lateral hole 50, where it is allowed to set. The liner 70 can then be disconnected from the drill pip 73 and the tool withdrawn from the borehole 14. If the liner 70 extends from the lateral hole 50, it may be necessary to mill the portion protruding from the borehole wall. This can be done with a special tool or with a suitable functional unit attached to the tool of the present invention.

Other completion options are also available, as follows:

-   -   a) The liner can be a slotted liner.     -   b) The completion can consist of a filter with gravel-pack.         Again, the packing gravel will be contained inside the filter         for the running in hole and pumped out in the same manner as         described above for cementing. In this case, it will be         necessary to provide a temporary liner inside the screen to         allow the pack to be pumped out of the end of the screen.     -   c) Intelligent completion with integrated valve and measurement         systems.

In some application, it may critical to perform multiple operations within one run in the main hole. One example could be the drilling of one lateral and installation of permanent sensor in the lateral.

For this application, a two head system can be used. Initially, the system is oriented so that the drill bit is facing the-proper direction for the lateral. After drilling, the orienting sub turns the drill head by 180 degrees (without the kick-pad). In this case, a clutch is provided to decouple (when required) the rotation of the drill head from the kick-pad. The other head is then positioned in front of the kick-pad, ready to enter the lateral hole. This can be the permanent installation system for the lateral, for example.

FIG. 8 shows an embodiment of the invention configured for multiple operations. The kick pad 42 is provided with a clutch system for rotation (or not) with the orienting sub 20 and the drilling motor. Furthermore, the kick pad can be equipped with two or more storage barrels 80, 81 to hold the motor and other functional elements items when unlatched.

For this application, the motor 38 is connected to the drill-pipe 36 by a latch system 82 controlled from the control sub 22. This allows unlatching of the motor 36 so as to be left in the large kick-pad barrel 80. The drill-pipe latch 82 can then be guided to another small barrel 80 in the kick pad 42. This small barrel 80 can be loaded with a different functional unit 84 terminated by a latch system 82. This allows the drill-pipe 36 to latch onto this item. The tool can then be used to push the functional unit 84 into the lateral hole 50 and install it permanently as described above (if required).

The present invention can also be adapted for use in cased hole. In such a use, a first trip to the proper location may be required with a mill to open a window in the casing, after which drilling and/or other operations can be conducted as described above.

When the tool is to be used through production tubing, variations may also be required. For example, a wireline fishable whipstock may be needed instead of the kick plate. Also, a tool such as a multi-finger calliper tool might replace the imaging tool used to locate the hole in the casing. 

1. A downhole tool comprising: (i) an axial drive unit (10) having a connection for an electric power cable extending up the borehole (14), and including anchoring mechanism operable in the borehole between a first configuration the which resists rotational and axial movement of the unit, and a second configuration in which the anchoring mechanism is moveable axially in the borehole, an axial drive mechanism that moves the anchoring mechanism axially down the borehole when in the second configuration; wherein the downhole tool further comprises: (ii) a motor mounted on the drive unit at the downhole end thereof; (iii) an hydraulic pump connected to the motor, the pump providing a source of hydraulic power; and (iv) a functional unit connected below the hydraulic pump and powered thereby, operation of the axial drive mechanism acting to move the functional unit axially down the borehole.
 2. A tool as claimed in claim 1, further comprising an orienting unit that allows axial rotation of at least part of the tool below the drive unit.
 3. A tool as claimed in claim 1, further comprising a diverting member positioned below the functional unit and which acts to urge the functional unit in a predetermined direction on operation of the drive mechanism.
 4. A tool as claimed in claim 1, wherein the hydraulic pump uses fluid in the borehole to provide the source of hydraulic power.
 5. A tool as claimed in claim 1, wherein the functional unit is a well construction device.
 6. A tool as claimed in claim 5, wherein the well construction device comprises a drilling assembly.
 7. A tool as claimed in claim 6, wherein the drilling assembly includes a drilling motor that is powered by the hydraulic power supply from the pump.
 8. A tool as claimed in claim 7, further comprising a drill bit that is drive by the drilling motor.
 9. A tool as claimed in claim 7, the drilling motor is connected to the pump by a hollow drill shaft through which the hydraulic fluid flows.
 10. A tool as claimed in claim 9, further comprising at least one support member mounted o the drill shaft to support against buckling when drilling.
 11. A tool as claimed in claim 6, further comprising at least one baffle arranged to direct drilled cuttings down the well below the tool.
 12. A tool as claimed in claim 6, further comprising a cuttings catcher positioned below the drilling unit and attached to the tool for catching material drilled by the drilling unit.
 13. A tool as claimed in claim 12, further comprising diverters located above and below the drilling unit to force the cuttings into the catcher.
 14. A tool as claimed in claim 13, further comprising a circulation tube extending between the diverters to allow fluid to circulate back up the borehole one the cuttings have been removed.
 15. A tool as claimed in claim 6, further comprising a measurement unit located in the drilling unit.
 16. A tool as claimed in claim 6, further comprising an inflatable packer above the drilling tool which, when inflated, allows pressure isolation of at least the portion of the borehole in which the drilling tool is located.
 17. A tool as claimed in claim 5, wherein the well construction unit comprises a completion unit.
 18. A tool as claimed in claim 17, wherein the well construction unit comprise a tubular completion member that can be advanced into the borehole by operation of the drive unit and disconnected so as to remain in place when the tool is withdrawn from the borehole.
 19. A tool as claimed in claim 18, wherein the completion member is filled with a completion fluid that is pumped out of the completion member and into the borehole around the completion member by means of the hydraulic pump.
 20. A tool as claimed in claim 1, further comprising a storage unit located in the borehole in which at least one functional unit can be stored when not in use.
 21. A tool as claimed in claim 20, further comprising a latching system for disconnecting the functional unit stored in the storage unit from the remainder of the tool.
 22. A tool as claimed in claim 1, further comprising an imaging device for locating the portion of the borehole at which the tool is to operate. 